1. Technical Field of the Invention
The present invention relates to a fuel injection device which injects a flat sector-shaped spray of fuel directly into the combustion chamber of an internal-combustion engine (hereinafter, the “internal-combustion engine” will simply be referred to as an “engine”).
2. Description of the Related Art
In recent years, direct-injection gasoline engines in which a fuel injection device injects fuel directly into an engine combustion chamber have been available. Generally, direct-injection gasoline engines were introduced in order to improve fuel efficiency and obtain a level of high power output. The spray shape of the fuel injected from the fuel injection device varies according to the specifications of the engine. In order to obtain a flat sector-shaped spray 308, as shown in FIGS. 22A and 22B, for example, a fuel injection device with a single flat sector-shaped injection hole 302 formed in a valve body 300 is known, in which the valve body 300 has a valve seat 304 and a nozzle needle 306 is seated on the valve seat 304.
The injection hole 302, however, is long in an injection direction because the hole 302 is formed in the valve body 300. Since it is difficult to form the injection hole 302 with press working, the injection hole 302 has to be formed with laser machining or electric discharge machining. However, there is a problem that machining time takes too long because the injection hole 302 is long in the injection direction. Also the fuel injection device has a low degree of flexibility in changing the shape of the spray 308, the concentration distribution of the spray 308 and the like, due to the single injection hole 302.
Japanese Patent Laid-Open Publication No. Hei 11-62787, as shown in FIGS. 23A and 23B, discloses a fuel injection device having a plurality of injection holes 311 formed in an orifice plate 310 to realize a flat sector-shaped spray 314. In this fuel injection device, however, the interval between the injection holes 311 is small, because the plurality of injection holes 311 are formed in a line within the limited area of the orifice plate 310. Since the fuel injection device of the direct-injection gasoline engine injects the fuel at a high pressure, as compared to a fuel injection device injecting fuel into an induction pipe, the narrow intervals between the injection holes 311 decrease the strength of the orifice plate 310 in an area where the injection holes 311 are formed, so that it is difficult for the plate 310 to endure the high fuel injection pressure. Additionally, the spray injected from the respective injection holes interfere and unite with each other due to the narrow intervals between the injection holes 311. It is impossible to inject the fuel from the respective injection holes in desired directions, so that there are many cases where the fuel is not injected in the desired shape.
Thickening the orifice plate 310 can increase the strength of the orifice plate 310, even if the interval between the injection holes 311 is narrow. When the orifice plate 310 is made thick, however, it becomes difficult to form the injection holes 311 by press working. In a case of machining the injection holes 311 by laser machining or electric discharge machining, a long machining time is necessary.
Thickening the orifice plate 310 makes the injection holes 311 long in the injection direction, so that fuel flow is rectified while flowing through the injection holes 311. The more turbulent the fuel flow passing through the injection holes 311 is, the greater the atomization will be of the spray 311 injected from the injection holes 311. Therefore, there is a problem that the fuel spray injected from the injection holes 311 is prevented from being atomized. That is, if the fuel flow is rectified while flowing through the lengthened injection holes 311.
An object of the present invention is to provide a fuel injection device for a direct-injection engine, which is easily manufactured with high strength, has a high degree of flexibility with regard to changing the concentration distribution or shape of a flat sector-shaped spray, and promotes the atomization of the fuel spray.